The wheel hub unit supports on one side a wheel of a vehicle and, in the case in which the wheel is driving, are angularly connected to a respective constant-velocity joint for the transmission of drive torque from the drive shaft to the wheel itself. The wheel hub assemblies have an axis of rotation and provide, or consist of, an inner ring and an outer ring coaxial with each other and to the axis of rotation and swivel relative to one another by the interposition between them of two crowns of rolling elements.
The inner ring has a flanged inner ring to allow the attachment of a wheel to the unit and between the inner ring and the outer ring are arranged with sealing devices to prevent the entry of external contaminants into the annular space delimited between the inner and outer rings and housing the rolling bodies.
The sealing device that is interposed between the inner and outer rings on the flange side of the wheel attachment is generally formed by a pair of rigid annular screens mounted coaxial to and facing, a first integral and a second integral with the outer ring to the inner ring and in use rotating with it. Typically the first screen door an annular sealing element, provided with one or more elastically deformable annular lips which cooperate in contacting manner and/or not contacting with the second screen.
Although satisfactory, this type of rolling bearings cannot ride out the leak test currently in use, in which a pressurized liquid jet is directed obliquely against the sealing device.